Sidestepping the principle of lawyer-client privacy, the Justice Department is letting investigators monitor phone calls and mail between some terrorist suspects and their defense lawyers.

A rule published Oct. 31 in the Federal Register says the monitoring can take place when Attorney General John Ashcroft concludes there is "reasonable suspicion" that the communications are related to future terrorist acts.

The rule, which took effect the day before it became public, is one of a series of steps by the Bush administration designed to make it easier to capture and prosecute terrorist suspects.

But the move has stunned many in the legal profession, which cherishes the absolute secrecy of conversations with clients.

"This proposal is a terrifying nightmare for innocent people who are under suspicion by the attorney general,'' said Laura W. Murphy, director of the national office of the American Civil Liberties Union.

New anti-terrorism laws give police sweeping new powers to secretly search people's homes and business records and to eavesdrop on telephone and computer conversations. The Social Security Administration's chief criminal investigator also is pressing for the right to disclose personal tax records, Social Security numbers and other data to law enforcement agencies.

The rule requires that any disclosures, except for those "necessary to thwart an imminent act of violence or terrorism," must be approved by a federal judge.

Declaring that the monitoring is not surreptitious, the rule also requires that the attorney and his client be given notice of the government's listening activities. In addition, a "privilege team" filters out confidential attorney-client information to ensure that investigators and prosecutors never see protected communications.

The government said it was necessary to put the rule in effect without public comment to allow the Justice Department to "respond to current intelligence and law enforcement concerns relating to threats to the national security or risks of terrorism."

The Federal Bureau of Prisons ordinarily sets up two types of phones for inmates — one in which calls are monitored and the other where inmates can talk in private with their lawyers. The monitored phones are prominently marked so that inmates know in advance that there is eavesdropping.

Phone calls from the designated monitored phones have been used in the past in criminal prosecutions — for example, in one of the cases against Webster Hubbell, a longtime friend of former President Clinton. Hubbell's phone calls in which he discussed his taxes were part of the framework for a tax evasion case against the former associate attorney general.

Some lawyers regard the Justice Department's move to allow monitoring of inmate-attorney communications as a step too far.

Lawrence Barcella, a former federal prosecutor and now a white-collar defense attorney in Washington, said the change chips away at the constitutionally protected attorney-client privilege, "which should give everyone pause."

"There is a very definite camel-with-his-nose-under-the-tent concern," Barcella said.

Prisoners see many of their constitutional rights curtailed while incarcerated, but generally not the guarantee of private communications with their lawyers, said Solomon L. Wisenberg, former deputy independent counsel to Whitewater prosecutor Ken Starr.

"This seems at first glance like a very troubling approach," he said.

Gerry Goldstein, past president of the National Association of Criminal Defense Lawyers, said it will inhibit criminal defendants from making plea agreements with prosecutors.

"What do you think monitoring does in terms of a client being honest and communicating in good faith with his lawyer?" Goldstein said. "When they know the government is listening, why would they ever talk about pleading guilty?"